There are connections but they aren't identical
A set of orbitals that can interact and delocalize is considered to be conjugated. These are usually pi systems, but there can be systems with sigma conjugation.
Resonance theory is a way to describe the way electrons interact when they are able to delocalize. It is an extension of the Lewis bonding theory, which allows the Lewis theory to describe systems where electrons can delocalize. Most of these are conjugated systems, most are conjugated pi systems, but resonance can be applied to sigma systems as well.
There are other, more advanced methods that can describe these delocalized systems more accurately - Molecular Orbital Theory and so on.